I flew Spirit from LAX to SFO with a layover in LAS, and it was one of the scariest flights I've ever been on. When the plane was getting ready to land, it hit a spotty area of heavy turbulence. When flying thousands of feet in the air, I expect some turbulence (whether I'm flying Virgin, Southwest, etc.), but I also expect to be informed and mentally prepared for the upcoming winds. The pilots were horrible about communicating with the passengers, and fellow passengers and I were quickly tightening our seat belts and grabbing onto the arm rests upon hitting the unexpected bumps. It was such an awful ride that the guy across the aisle from me got motion sickness and vomited.
There are so many other negative things I can say about my experience on Spirit, but I think the previous Yelpers can also paint a pretty vivid picture....Simply, AVOID FLYING SPIRIT!